Here would be my suggestions, from someone who used to be very unsure about oral (but now loves it).
Sorry about the gendered language but I can only write this from a cis/het perspective.
Don’t head straight for her genitals. (Remember you are making love to a whole person not just an orifice). She is more likely to be open to the idea if she is really warmed up first. Take your time.
Many women’s insecurities about oral stem from the feeling that female genitals are ugly and shameful and therefore must be hidden away. Society reinforces this idea from an early age. Having someone look right at them (as they must during oral) can be terrifying. Tell her how much you like how she looks down there, how her scent turns you on, and how much you love to touch her there. Do this whether or not you go on to anything further. It may take some time before she actually believes you.
Another thing that may be putting her off is the worry that she might cum too quickly with oral stimulation (and then not be able to have an orgasm if you go on to PIV later). Or, she might be worried about NOT being able to cum with oral and therefore upsetting you, or how her cumming will feel/taste for you. These fears held me back for a long time!! Reassure her that whatever happens, it’s OK.
Maybe this one is just me but I like the room to be warm enough for us both to be mostly uncovered. I hate it if OH just disappears under the bedclothes, I feel like I’ve been abandoned….I need to be able to see him and touch him, and for him to be touching me at other places than just my genitals. So use your hands all over her body. Love her everywhere.
Finally, it’s not really about specific techniques. Everyone likes different things - you’ll just have to keep checking in to find out what she likes/doesn’t like. She may not use words - pay attention to the way she moves and the sounds she makes.
Good luck!